1. Field of the Invention
The invention relates to semiconductor processing equipment and, more particularly, the invention relates to ceramic substrate supports.
2. Description of the Background Art
Susceptors are widely used to retain substrates, such as semiconductor wafers, in semiconductor wafer processing systems during processing. The susceptor is typically mounted to a pedestal. The pedestal is typically fabricated from a metal such as aluminum. For high temperature applications, the susceptor is typically fabricated from a ceramic material such as aluminum oxide or aluminum nitride. The susceptor typically contains various components which provide heating and/or cooling of the wafer as well as clamping (chucking) of the wafer to retain the wafer in a stationary position upon the pedestal surface. The pedestal may also include one or more electrodes for applying a bias voltage to the wafer. Such a bias voltage may be a direct current (DC) bias or a radio frequency (RF) bias.
Electrostatic susceptors (or chucks) retain a substrate by creating an electrostatic attractive force between the workpiece and the chuck. A voltage applied to one or more electrodes in the chuck so induces opposite polarity charges in the workpiece and electrodes. The opposite charges pull the workpiece against the chuck, thereby retaining the workpiece. These chucks find use in different types of wafer processing including etching, chemical vapor deposition (CVD), and physical vapor deposition (PVD) applications. Examples of monopolar and bipolar electrostatic chucks can be found in U.S. Pat. Nos. 5,745,332 and 5,764,471 respectively and are herein incorporated by reference.
The materials and processes used to process a semiconductor wafer are temperature sensitive. Should these materials be exposed to excessive temperature fluctuations due to poor heat transfer from the wafer during processing, performance of the wafer processing system may be compromised. To optimally transfer heat between the wafer and the chuck (or vice versa), an electrostatic force created by the applied voltage causes a large amount of wafer surface to physically contact a support surface of the chuck. However, due to surface roughness of both the wafer and the chuck, small interstitial spaces remain between the chuck and wafer that interfere with optimal heat transfer.
To promote uniform heat transfer characteristics, an inert heat transfer gas (e.g., Helium, Argon, hydrogen, and the like) is introduced beneath the wafer to fill the interstitial spaces between the wafer and the chuck surface. This gas acts as a thermal conduction medium between the wafer and the chuck, and is commonly known as a wafer xe2x80x9cbackside gasxe2x80x9d. Moreover, the heat transfer gas has better heat transfer characteristics than the vacuum that exists in the chamber during wafer processing, thereby promoting uniform heat conduction across the entire bottom (i.e., backside) surface of the wafer. Such a heat transfer gas is typically provided by ports provided through the body of the chuck from the wafer support surface to the bottom of the chuck. However, when the chuck is subject to a plasma (i.e., during a particular wafer processing step or chamber cleaning step), the heat transfer gas is prone to ignition thereby generating a plasma in the ports. The plasma in the ports sputters ceramic particles off of the walls of the ports. The sputtered particles enter and contaminate the processing chamber and/or the wafer.
Techniques, such as the use of porous plugs and narrow diameter ports, have been employed to prevent plasma ignition. Specifically, the porous plugs and narrow, high aspect ratio ports are designed to cause electrons that are present during processing to become neutralized (or quenched) upon colliding with the walls or the plugs or ports before encountering a gaseous (He) atom, thereby preventing plasma formation within the ports. Although these techniques do inhibit plasma ignition in the ports, they do have drawbacks. For example, the use of porous ceramic plugs complicates the fabrication of the chuck. Furthermore, porous ceramics tend to be chalky and produce particles that also contaminate wafers during processing. Additionally, for the range of heat transfer gas pressure and electric fields normally encountered in the heat transfer gas ports, the diameter of the hole should be as small as possible. However, it is extremely difficult, time consuming, and expensive to manufacture a ceramic chuck with small diameter holes bored entirely through the chuck body. Holes greater than 3 millimeters (mm) in diameter can be drilled in ceramics relatively easily using diamond drills. Holes 0.5 mm in diameter can be drilled through 3-15 mm of ceramic, at great expense, only by ultrasonic drilling methods. Unfortunately, the optimal hole diameter to eliminate plasma ignition is typically about 0.2 mm. Such holes can only be drilled through a thick plate by expensive laser drilling. Since the heat transfer gas flow rate depends on the overall area of the holes, many small diameter holes (hundreds) are required to feed the heat transfer gas fast enough to achieve the desired heat exchange.
Another technique includes forming a plenum (i.e., one or more radial gas channels and a circumferential groove) in an uncured, ceramic green-body tape layer below the support surface. Additional layers are similarly formed thereabove with desired features such as heat transfer gas distribution ports, lift pin holes and/or provided with other susceptor components such as electrodes. All the layers are then sintered to form a unitary ceramic susceptor having all of the desired features. Unfortunately, the tremendous pressure exerted on the layers during the sintering process (on the order of 100-1000 psi) tends to deform or even collapse some of the features such as the plenum. As such, the features are not highly repeatable during the manufacturing of the susceptor. That is, the features do not have the same dimensions or quality when comparing one susceptor to another. Filler pastes are added to the features of the uncured ceramic, but such pastes do not completely eliminate deformation or avoid collapsing. Additionally, once the filler pastes are added, an extra heating step is required to carbonize the filler thereby removing it from the features.
Therefore, a need exists in the art for an easily fabricated ceramic electrostatic chuck having a heat transfer gas distribution structure that inhibits plasma ignition in the gas delivery channels and a concomitant method of fabricating the same.
The disadvantages associated with the prior art are overcome by the present invention of a method of fabricating a semiconductor wafer support chuck apparatus having a first sintered layer and a second sintered layer. The method comprising the steps of providing the first sintered layer having a plurality of gas distribution ports and providing the second sintered layer having a plurality of grooves. The first sintered layer is stacked on top of the second sintered layer, where a diffusion bonding layer is disposed between the first sintered layer and the second sintered layer. Thereafter, the stacked first and second sintered layers are resintered such that the diffusion bonding layer joins the first and second sintered layers together to form a semiconductor wafer support apparatus.